In: Chemistry
1.Why doesn’t initiation occur in the micelles in emulsion polymerization?
2.Describe a gel for drug release.
1.
Conventional emulsion polymerization is a process in which a monomer (or mixture of monomers) dispersed in aqueous phase (or other means of disperson) is converted through a free radical polymerization into a "kinetically stable" dispersion of polymer particles of smaller diameter than a micron.
The mechanism that occurs in emulsion polymerization is as follows:
A monomer is dispersed (emulsified) in a solution of surfactant and water forming relatively large droplets of monomer in water.
Excess surfactant creates micelles in the water.
Small amounts of monomer diffuse through the water to the micelle.
A water soluble initiator is introduced into the aqueous phase where it reacts with the monomer in the micelles.
The total surface area of the micelles is much larger than the total surface area of the monomer droplets, therefore, the initiator typically reacts in the micelle and not in the monomer.
The monomer in the micelle polymerizes rapidly and the growing chain ends. At this point the monomer swollen micelle has become a polymer particle.
More monomer derived from the droplets diffuses to the growing particle, where more initiators will eventually react.
Finally, the free monomer droplets disappear and all the remaining monomer is found in the particles.
2.
From the point of view of materials, the trend is to get intelligent systems, loaded with the active substance of the medicine, which respond to environmental stimuli and can release their burden on the place, time and at the desired speed. That is how in recent decades polymers have received a lot attention for its application in this given area that its properties can be designed according to the requirements that are desired to meet the medication release needs. Between polymers, hydrogels have shown very good properties to be loaded with medications, for being biocompatible and presenting properties swelling in aqueous medium among others characteristics of interest, which profiled them as a good option to be used in controlled release of medications.
A hydrogel is a three-dimensional network made up of fl exible chains of polymers that absorb amounts considerable water. These polymers have well-known characteristics, such as being hydrophilic, soft, elastic and water insoluble in addition to that swell in her presence, increasing appreciably its volume while maintaining the form until reaching the chemical physical balance. Additionally, they can have great resistance mechanics according to the method with which they are obtained.
Hydrogels are very appropriate materials for applications in medicine given its good interaction with living tissues, since on the one hand they show good biocompatibility properties, due mainly to its soft, elastic consistency and water content On the other hand, they are materials inert so cells and proteins do not tend to stick to its surface. And also, its characteristic of swelling in liquid medium gives them the property of absorb, retain and release under controlled conditions, some organic solutions.
In the application as medication releasers, hydrogels have been widely used as intelligent carriers of active substances, and its physical and chemical characteristics such as capacity swelling, release kinetics, response to environment or biodegradability, have been worked by the engineering to molecular levels in order to achieve its optimization.
All of the above considerations determine the physical and chemical properties of the resulting hydrogel and they must be taken into account in the design, synthesis and Application of polymeric release systems active substances Taking these aspects into account is what which will allow to promote other applications of this new generation of biomaterials in medical areas, pharmaceutical or biological.